Post-collisional high-Mg granitoids from the Paleoproterozoic East Sarmatian Orogen (East European Craton): Evidence for crust–mantle interaction R.A. Terentiev a, ⁎, M. Santosh b,c,d a Department of Geology, Voronezh State University, Russia b Centre for Tectonics, Resources and Exploration, Department of Earth Sciences, University of Adelaide, SA 5005, Australia c School of Earth Sciences and Resources, China University of Geosciences Beijing, 29 Xueyuan Road, Beijing 100083, China d Department of Geology, Northwest University, Northern Taibai Str. 229, Xi'an 710069, China abstract article info Article history: Received 17 October 2016 Accepted 3 January 2017 Available online 14 January 2017 The East Sarmatian Orogen (ESO) is located along the southwestern domain of the East European Craton and occupies a key tectonic link between the Sarmatian and Volgo-Uralian domains. Here we investigate the Paleoproterozoic Novaya Melovatka pluton and its mafic-ultramafic xenoliths to gain insights into the role of interaction between intermediate–felsic crustal melt with mantle rocks as a mechanism for the generation of high-Mg granitoids at crustal pressures. The pluton is composed of biotite-orthopyroxene quartz dioritic and monzodioritic porphyrites (Phase 1) and medium-grained biotite-amphibole quartz diorite, tonalite and granodiorite and commingled Phase 1 mafic magmatic enclaves (MME) (Phase 2). The general geochemical characteristics of these rocks are similar to those of Late-Archean high-Mg sanukitoids. The T DM (model) ages for intermediate Phase 1 and granitoid Phase 2 are similar and show a range of 2324–2439 and 2284–2519 M, respectively. The εNd(t) values are grouped around subchondritic values (=+1.4–+1.9 and +1.1–+2.2) and the initial 87 Sr/ 86 Sr ratios are in the range of 0.70202–0.70390. The complex compositional zoning of minerals suggests that the rocks crystallized as synchronous but discrete magma pulses, with limited to significant mixing. Based on the geochemical features we infer that the Phase 1 rocks formed from partial melting of a mantle wedge metasomatized to different degrees by fluids/melts. The presence of MMEs, compositional zoning of minerals including reversely zoned amphiboles, plagioclases with thin calcic overgrowths, and acicular apatite, as well as the whole-rock geochemical features are consistent with a hybrid origin of the high-Mg granitoids belonging to Phase 2. Geobarometry indicates crystallization at upper-crustal depths (i.e. 1.7–2.4 kbar). The igneous suite evolved by fractional crystallization of orthopyroxene, hornblende, plagioclase and biotite. Here we propose a tectonic model involving partial melting of the lower crust that produced low-Mg melts which interacted with high-Mg mantle melts derived from previously underplated source. © 2017 Elsevier B.V. All rights reserved. Keywords: Crust–mantle interaction East Sarmatian Orogen Geochemistry Magma mixing Tectonics 1. Introduction High-Mg granitoids (sanukitoids) were identified in the 1980s (Shirey and Hanson, 1984) as a geochemically distinct suite from the more common tonalite–granodiorite–trondhjemite (TTG) suites in Archean terranes. Compared with the TTG suite, high-Mg granitoids are enriched in Mg, Ni, Cr, Ba, Sr and LREE (Heilimo et al., 2010; Shirey and Hanson, 1984) and are associated with the suite of diorites, quartz diorites, monzodiorites, quartz monzodiorites and granodiorites (Martin et al., 2005) to monzogranites (Heilimo et al., 2010), together with subordinate tonalitic varieties. The contrasting “crustal” and “mantle” isotopic and geochemical characteristics of sanukitoids have been interpreted to indicate melting of an enriched mantle source (Halla, 2005; Heilimo et al., 2010; Martin et al., 2005; Stevenson et al., 1999), although the mechanisms for this remain debated. On the other hand, the enrichment of high-Mg diorites/granite in LREE, Ba, Sr, as compared to typical calc-alkaline granitoids has been interpreted as an evidence for crustal origin of the former, as a result of crustal contam- ination (e.g., Henry et al., 1998; Stevenson et al., 1999) or are thought to come from an enriched mantle (e.g., Halla et al., 2009). Although the mechanisms of crustal contamination in sanukitoid genesis are not fully understood (Halla, 2005), a crustal contribution has been well- established for felsic sanukitoids (e.g., Lobach-Zhuchenko et al., 2005). Some of the key isotopic characteristics, including mantle values for εNd(T) and εHf(T) (Corfu and Stott, 1996) and crustal signature of Sr and Pb isotopes (Stevenson et al., 1999), are also topics of debate in Lithos 274–275 (2017) 271–290 ⁎ Corresponding author at: Voronezh State University, University Square, 1, off. 204p, 394018, Russia. E-mail address: terentiev@geol.vsu.ru (R.A. Terentiev). http://dx.doi.org/10.1016/j.lithos.2017.01.004 0024-4937/© 2017 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos